The present invention generally relates to rotary recording medium reproducing apparatuses, and more particularly to a rotary recording medium reproducing apparatus which puts a tracking control system in a nonoperational state during a mode such as a search mode in which tracking of a reproducing element is not required.
Systems have been realized in which a recording system forms pits in accordance with information signal being recorded along a spiral track on a flat rotary recording medium (hereinafter referred to as disc), without forming a groove therein, and a reproducing stylus traces over along this track to reproduce the recorded information signal in response to variations in the electrostatic capacitance in a reproducing system.
In this system, since no groove is provided on the disc for guiding the reproducing stylus, pilot or reference signals are recorded on or in the vicinity of a track of the information signal, such as a video signal, on the disc. Upon reproduction, the reference signals are reproduced together with the video signal. Tracking servo control is carried out so that the reproducing stylus accurately traces along the track in response to the reproduced reference signals.
In the above disc, only one of a first and second reference signals fp1 and fp2 is recorded at an intermediate position between center lines of adjacent track turns. Moreover, the side on which the first and second reference signals are recorded with respect to one track turn changes over every one track turn. That is, when the first and second reference signals are respectively recorded on the right and left sides of one track turn, the relationship between the recorded positions of the reference signals is such that the second and first reference signals are respectively recorded on the right and left sides of adjacent track turns. Furthermore, a third reference signal for obtaining a changeover signal upon reproduction, is recorded for every track turn at recording changeover positions of the above first and second reference signals.
In a reproducing apparatus, a changeover operation is performed by use of the third reference signal reproduced upon obtaining of a tracking control signal from the reproduced first and second reference signals.
Since no grooves are provided in the above disc, the reproducing stylus can be transferred from one track to another without damaging the reproducing stylus or the disc. Accordingly, in addition to the special reproduction such as still reproduction, slow-motion reproduction, and quick-motion reproduction, the system is capable of performing a so-called random access such as a high-speed search in which the reproducing stylus is transferred to a desired position at high speed to reproduce the desired information.
However, when a tracking control system is left in an operational state during a random access mode in which a reproducing transducer having the above reproducing stylus is transferred at a high speed, the reproducing stylus is controlled to trace over one track to the limit of resiliency of a resilient support member which supports a cantilever provided with the reproducing stylus, as a reproducing transducer main body is transferred. When the deformation of the resilient support member exceeds the limit of resiliency, the reproducing stylus follows the reproducing transducer main body which is being transferred due to the resilient force to skip over a plurality of tracks, and is again controlled so as to trace over one track. The above operation is repeatedly performed, and as a result, the resilient support member is deformed to the limit of resiliency and restored repeatedly within a substantially short period. Accordingly, the resilient support member is easily damaged due to wear. Moreover, since the reproducing stylus is instantaneously swung after being inclined to trace the tracks, the reproducing stylus is also quickly damaged due to wear.
During the above random access mode, there is no need to reproduce the main information signal such as the video signal, since the only requirement is for the reproducing transducer to reach a desired position on the disc at a high speed. Hence, there is no need to perform tracking control operation, during the above random access mode. Even when the tracking control operation is not performed, for example, a chapter address signal recorded at vertical synchronizing signal positions can be reproduced once for every some number of tracks. Accordingly, random access and the like in which the reproducing stylus is transferred to a target position by use of the reproduced address signal, can be positively performed.
Therefore, during a mode such as a random access mode, it is desirable not to perform the tracking control operation, in order to prevent premature wear of the above reproducing stylus and the resilient support member.
In a previously devised rotary recording medium reproducing apparatus for realization, a switch circuit for muting is provided in a circuit system which supplies a tracking control signal obtained by use of the reproduced first and second reference signals fp1 and fp2 to a tracking control coil of the reproducing transducer. Accordingly, in this reproducing apparatus, the above switch circuit is opened by a muting signal obtained from a micro-computer during a random access mode, to interrupt the supply of the tracking control signal with respect to the tracking control coil.
On the other hand, the above circuit system for obtaining the tracking control signal from the first and second reference signals comprises, a wave detection circuit for respectively and independently wave-detecting the first and second reference signals, a changeover circuit for alternately changing over the reproduced first and second reference signals every one revolution of the disc to supply the reference signal to the wave detection circuit, a time constant circuit connected to an output side of the wave detection circuit, and a differential amplifier supplied with an output of the time constant circuit for producing a control signal according to a level difference. The above switch circuit for muting is connected to an output side of the differential amplifier. The above time constant circuit consists of a lowpass filter for eliminating an unwanted signal component within an output signal of the wave detection circuit, and a circuit for holding the wave detected output obtained with a horizontal scanning period. Concretely, the above time constant circuit is constructed from resistors and a capacitor.
However, upon starting of a random access mode, even when the above switch circuit for muting is opened in order to interrupt the tracking control signal, a large error voltage remains within the time constant circuit since the capacitor of the above time constant circuit continues to be charged. Accordingly, after the above random access is performed and the reproducing transducer has reached a desired position, when the above switch circuit is closed in order to perform normal reproduction from that position maintaining tracking control, an unwanted control signal which is formed according to the large charged voltage left within the time constant circuit is applied to the tracking control coil. Since the charged voltage before closing of the switch circuit is substantially different from a voltage corresponding to tracking control after completion of the random access operation, even in a case where the reproducing stylus stops at the correct position, the reproducing stylus is shifted from the correct position due to the above unwanted control signal. Therefore, there was a disadvantage in that a certain time was required until the correct tracking control signal is obtained to perform the correct tracking operation.
Furthermore, by the above circuit construction, a plurality of circuit elements are required due to the switch circuit for muting which is provided. In addition, there was a disadvantage in that an output port exclusively for the muting signal was required in the micro-computer.